Over the last decades, the dimensions of micro-electronic devices have been continuously scaled down, leading to exponential gains in computational power and reduction in production cost. However, as the device dimensions are shrinking to the order of 10 nm, further scaling brings significant challenges to optical lithography. These challenges include not only the issue of resolution, but additionally the accurate pattern placement, i.e., the alignment of features to already existing features on the substrate, is emerging as a major concern for the conventional “top-down” patterning techniques.
An alternative approach that is gaining increasing importance is based on “bottom-up” strategies for patterning. Examples include self-aligned vias, self-aligned double and multiple patterning, directed self-assembly (DSA), and area selective deposition. In area selective deposition, differences in surface reactivity are exploited to deposit material only according to predefined patterns, while the rest of the substrate remains unaffected. This can enable self-aligned processing, as the selectively grown film is aligned to a pre-existing pattern.
The approaches for area selective deposition that have previously been explored typically rely on the grafting of the area where deposition should be prevented with self-assembled monolayers (SAMs) or macromolecules combined with atomic layer deposition (ALD). This is for instance the case in Hashemi et al. (ACS applied materials & interfaces, vol. 8, issue 48, pages 33264-33272). In ALD, a thin film is deposited on a substrate by self-limiting surface reactions of gas phase precursors. The deposition principle, based exclusively on surface reactions, provides an excellent opportunity to exploit area selective deposition. However, thermal ALD processes, which are compatible with the selectivity concept, are mostly limited to the deposition of metal oxides or metal nitrides, which are high-k materials. In addition, the ALD process conditions, such as temperature, precursors, and oxidizing environment, can typically have a detrimental effect on the other materials comprised in the substrate, such as on any organic materials.
There is thus still a need for methods for area selective deposition that address some or all of the issues described above.